The present disclosure relates, in various exemplary embodiments, to toner compositions and processes thereof. More specifically, the present disclosure relates to low melt toner compositions comprising a mixture of a branched amorphous polyester resin, a crystalline polyester resin, a colorant, and optionally a wax. Additionally, the present exemplary embodiments relate to processes for forming such toner compositions. This disclosure finds particular application in conjunction with xerographic or electrostatographic printing processes, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
Crystalline and branched resins are known. For example, crystalline refers to a polymer with a 3 dimensional order, and branched refers to a polymer with chains linked to form a crosslinked network.
Xerographic toners of a resin, a pigment, and a charge control agent are known. Toners useful for xerographic applications should exhibit certain performances related to storage stability, and particle size integrity, that is, it is desired to have the particles remain intact and not agglomerate until they are fused on paper. Since environmental conditions vary, the toners also should not substantially agglomerate up to a temperature of from about 50° C. to about 55° C. The toner composite of resins and colorant should also display acceptable triboelectrification properties which vary with the type of carrier or developer composition. A valuable toner attribute is the relative humidity sensitivity ratio, that is, the ability of a toner to exhibit similar charging behavior at different environmental conditions such as high humidity or low humidity. Typically, the relative humidity of toners is considered as the ratio between the toner charge at 80 percent humidity divided by the toner charge at 20 percent humidity. Acceptable values for relative humidity sensitivity of toner vary, and are dependant on the xerographic engine and the environment. Typically, the relative humidity sensitivity ratio of toners is expected to be at least 0.5 and preferable 1.
Another important property for xerographic toner compositions is its fusing properties on paper. Due to energy conservation measures, and more stringent energy characteristics placed on xerographic engines, such as on xerographic fusers, there has been pressure to reduce the fixing temperatures of toners onto paper, such as achieving fixing temperatures of from about 90° to about 120° C., to permit less power consumption and allowing the fuser system to possess extended lifetimes. For a noncontact fuser, that is a fuser that provides heat to the toner image on paper by radiant heat, the fuser usually is not in contact with the paper and the image. For a contact fuser, that is a fuser which is in contact with the paper and the image, the toners should not substantially transfer or offset onto the fuser roller, referred to as hot or cold offset depending on whether the temperature is below the fixing temperature of the paper (cold offset), or whether the toner offsets onto a fuser roller at a temperature above the fixing temperature of the toner (hot offset).
Another desirable characteristic is sufficient release of the paper image from the fuser roll. For oil containing fuser rolls, the toner compositions may not contain a wax. For fusers without oil on the fuser (usually hard rolls), however, the toner composites will usually contain a lubricant like a wax to provide release and stripping properties. Thus, a toner characteristic for contact fusing applications is that the fusing latitude, that is the temperature difference between the fixing temperature and the temperature at which the toner offsets onto the fuser, should be from about 30° C. to about 90° C., and preferably from about 50° C. to about 90° C. Additionally, depending on the xerographic applications, other toner characteristics may be desired, such as providing high gloss images, such as from about 60 to about 80 Cardner gloss units, especially in pictorial color applications.
Other toner characteristics relate to nondocument offset, that is, the ability of paper images not to transfer onto adjacent paper images when stacked up, at a temperature of about 55° C. to about 60° C.; nonvinyl offset properties; high image projection efficiency when fused on transparencies, such as from about 75 to about 100 percent projection efficiency and preferably from about 85 to 100 percent projection efficiency. The projection efficiency of toners can be directly related to the transparency of the resin utilized, and clear resins are desired.
Additionally, small sized toner particles, such as from about 3 to about 12 microns, and preferably from about 5 to about 7 microns, are desired, especially in xerographic engines wherein high resolution is a characteristic. Toners with the aforementioned small sizes can be economically prepared by chemical processes, also known as direct or “in Situ” toner process, and which process involves the direct conversion of emulsion sized particles to toner composites by aggregation and coalescence, or by suspension, microsuspension or microencapsulation processes.
Toner compositions are known, such as those disclosed in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference, and wherein there are illustrated toner compositions comprised of a thermotropic liquid crystalline resin with narrow melting temperature intervals, and wherein there is a sharp decrease in the melt viscosity about the melting point of the toner resin particles, thereby enabling matte finishes. The aforementioned toners of the '313 patent possess sharp melting points and can be designed for non-contact fusers such as Xenon flash lamp fusers generating 1.1 microsecond light pulses. For contact fusing applications, sharp melting materials can offset onto the fuser rolls, and thus the toners of the '313 patent may possess undesirable fusing latitude properties.
In U.S. Pat. No. 4,891,293, there are disclosed toner compositions with thermotropic liquid crystalline copolymers, and wherein sharp melting toners are illustrated. Moreover, in U.S. Pat. No. 4,973,539 there are disclosed toner compositions with crosslinked thermotropic liquid crystalline polymers with improved melting characteristics as compared, for example, to the thermotropic liquid crystalline resins of the '313 or '293 patents.
Furthermore, it is known that liquid crystalline resins may be opaque and not clear, and hence such toners are believed to result in poor projection efficiencies. The toners of the present exemplary embodiment in contrast are comprised of a crystalline resin with sharp melting characteristics, and a branched resin with a broad molecular weight, and wherein there are permitted fusing characteristics, such as lower fixing temperatures of from about 90° C. to about 120° C. and a broad fusing latitude of from about 50° C. to about 90° C., with contact fusers with or without oil. Furthermore, a crystalline portion of from about 5 to about 40 percent of the toner is believed to be dispersed in small domains within the amorphous and clear branched resin, and with domain diameter sizes of, for example, less than or equal to about 100 to about 2,000 nanometers, and more specifically, from about 50 to about 300 nanometers, and such that the high projection efficiency is maintained. Thus, while the crystalline resins employed in the toner particles of the present disclosure are also opaque, high projection efficiency is maintained because, without being bound to any particular theory, resin is dispersed in the branched resin with sizes of about less than 300-400 nanometers. Projection efficiencies of from about 70 to about 90 percent may be maintained depending on the colorant used.
Low fixing toners comprised of semicrystalline resins are also known, such as those disclosed in U.S. Pat. No. 5,166,026, and wherein toners comprised of a semicrystalline copolymer resin, such as poly(alpha-olefin) copolymer resins, with a melting point of from about 30° C. to about 100° C., and containing functional groups comprising hydroxy, carboxy, amino, amido, ammonium or halo, and pigment particles, are disclosed. Similarly, in U.S. Pat. No. 4,952,477, toner compositions comprised of resin particles selected from the group consisting of semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C., and containing functional groups comprising hydroxy, carboxy, amino, amido, ammonium or halo, and pigment particles, are disclosed. Similarly, in U.S. Pat. No. 4,952,477, toner compositions comprised of resin particles selected from the group consisting of semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C. and pigment particles are disclosed. Although, it is indicated that some of these toners may provide low fixing temperatures of about 200° F. to about 225° F. (degrees Fahrenheit) using contact fusing applications, the resins are derived from components with melting characteristics of about 30° C. to about 50° C., and which resins are not believed to exhibit more desirable melting characteristics, such as about 55° C. to about 60° C.
In U.S. Pat. No. 4,990,424 toners comprised of a blend of resin particles containing styrene polymers or polyesters, and components selected from the group consisting of semicrystalline polyolefin and copolymers thereof with a melting point of from about 50° C. to about 100° C. are disclosed. Fusing temperatures of from about 250° F. to about 330° F. (degrees Fahrenheit) are reported.
Low fixing crystalline based toners are disclosed in U.S. Pat. No. 6,413,691, and wherein a toner comprised of a binder resin and a colorant, the binder resin containing a crystalline polyester containing a carboxylic acid of two or more valences having a sulfonic acid group as a monomer component, are illustrated. The crystalline resins of the '691 patent are believed to be opaque, resulting in low projection efficiency.
Crystalline based toners are disclosed in U.S. Pat. No. 4,254,207. Low fixing toners comprised of crosslinked crystalline resin and amorphous polyester resin are illustrated in U.S. Pat. Nos. 5,147,747 and 5,057,392, and wherein the toner powder is comprised, for example, of polymer particles of partially carboxylated crystalline polyester and partially carboxylated amorphous polyester that has been crosslinked together at elevated temperature with the aid of an epoxy novolac resin and a crosslinking catalyst.
Copending U.S. patent application Ser. No. 10/349,548, which is published as U.S. Patent Application No. U.S. 2004/0142266, is directed to toner compositions comprising amorphous polyester resins and crystalline polyester resins and a process for making such toners. The present disclosure is directed to a new process for making toners comprising amorphous polyester resins and crystalline polyester resins. Additionally, the present disclosure is directed to toners comprising lithio-sulfonated branched polyester resins and lithio-sulfonated crystalline polyester resins.
Also of interest are U.S. Pat. Nos. 6,383,205 and 4,385,107, the disclosures of which are totally incorporated herein by reference.
Polyester based emulsion/aggregation resins comprising a combination of a first resin component with a second resin component having significantly different melt flow properties than the first resin (such as a sharp melting crystalline resin) may be prepared via direct coalescence method or process. Forming such toners by direct coalescence, however, may be limited in terms of particle growth control, morphology and yields (generally providing low yields).
There is thus a need to provide low melt and ultra low melt toners. There is thus also a need to provide a process for preparing such low melt emulsion aggregation toners that allows for controlled particle growth, controlling morphology or shape, and provides high yields.